The research program is a study of synaptic transmission in the vertebrate retina. The experiments will combine optical and electrophysiological methods. Complementary experiments will investigate vesicle cycling in dissociated cells and the transmission between identified cells in a retinal slice. The experiments will use mammalian and, when possible, non-mammalian preparations. Five specific aims are proposed: (1) to determine the Ca2+ dependence of synaptic vesicle cycling (in mammalian cones); (2) to determine if continuous and transient vesicle cycling are produced by a common molecular mechanism (in bipolar cells); (3) to determine the role of intracellular Ca2+ stores in transmitter release (from rod photoreceptors and bipolar cells); (4) to determine the role of a cGMP-gated current in transmitter release (from cone photoreceptors); and (5) to determine if mammalian cone photoreceptors release transmitter at basal junctions.